Fluid control valves such as butterfly type valves, are utilized extensively in petroleum processing and pipeline systems. In such systems, the normal high operating reliability requirement of the fluid seal, i.e. positive shutoff and low breakaway (opening) torque is compounded by the further requirement that the seal continue to operate satisfactorily in fire conditions involving high temperatures and high pressures.
In Simmons, et al., U.S. Pat. No. 4,113,268, there is provided a fire proof, bubble-tight sealing mechanism which utilizes a two-stage arrangement. A soft primary seal, for example of Teflon, is inserted in the rib of a metal seal ring for contact with the complimentary surface of a closure member. The Teflon material, extending radially inward beyond the metal rib, provides a bubble-tight seal under normal conditions. In the event of fire, the Teflon is destroyed. Subsequently, the metal rib of the seal ring dynamically moves into position to form a secondary or metal to metal seal.
While the Simmons, et al. invention was a major advance in the art, which provided an unprecedented quality of sealing and fire safety in a butterfly valve, certain drawbacks nevertheless exist. The primary seal necessitates the machining of a metal and the insertion of a soft material into the metal rib of the seal ring, the insertion thereof which is a relatively difficult and expensive manufacturing procedure.
Benware in U.S. Pat. No. 3,642,248, discloses a valve sealing mechanism wherein the seal ring is fitted within a circumferential groove of a valve body member. A portion of the seal ring extends out of the groove, radially inward, for making engagement with a closure member or disc. The seal ring is arranged within the groove for movable adjustment in response to the pressure of the system.
The seal ring of Benware, in a preferred embodiment, has a backing ring which is held within a groove, beneath the seal ring. This backing ring provides a pre-loaded sealing force for the sidesealing of the seal ring within the walls of the groove.
The seal ring of Benware is preferably constructed of a soft material such as Teflon. However, a second embodiment discloses a metal seal ring. In the latter, a pair of inclined surfaces at the sides of the steel ring abuts the lateral sides of the groove and are pre-loaded by being of a slightly greater dimension than the width of the groove. The front of the seal ring is curved slightly and concavely in relation to the disc surface. This causes the upstream and downstream edges of the seating surface of the seal ring to bite against the disc surface when the seal ring is pushed against the disc.
This metal seal ring of Benware has proved unsatisfactory. Although the seal ring is constructed of metal for fire safe performance, the metal to metal contact does not provide the desired quality and reliability of sealing for the desired use of such valves. Sahba, et al., in U.S. Pat. No. 4,744,572 discloses a metal seal ring which is an improvement of the metal seal ring disclosed in Benware, U.S. Pat. No. 3,642,248. In Sahba, U.S. Pat. No. 4,744,572, there is provided a seal ring positioned within a groove circumferential with respect to the passageway of the valve. A convex seating portion of the seal ring extends through an annular opening in the groove, for sealing engagement with a closure member. Shoulder portions, which extend from the sides of the seating portion, abut the side walls of the groove. The seal ring is compressed in width within the groove, so that a resilient side-sealing force is imparted to the contact of the shoulder portions with the side walls of the groove.
While the metal seal ring of Sahba, et al. has proved commercially successful, it is desired to improve the quality and reliability of such sealing mechanisms.
Other seal mechanisms as shown in Wucik, Jr., et al. U.S. Pat. No. 3,986,699, include a metal valve seat insert ring having an inner thin-walled skirt-like lip for making pre-loaded sealing contact with a valve disc. The edge of the lip engages a mating circumferential sealing surface of a valve disc, at a location downstream from the plane of maximum disc diameter, with an interference fit to provide a pre-loaded radial sealing force between the edge of the lip and the sealing surface of the disc. The annular lip forms the downstream side of an undercut groove for a resilient seal ring that provides a primary seal, and the engagement of the lip edge with the sealing surface of the valve member provides a metal-to-metal backup seal in the event of damage to or destruction of the resilient seal ring.
It is desired to provide an improved seal for rotary type fluid control valves which eliminates the problems of prior seals, provides a reliable and positive shutoff seal on closing, and requires a small breakaway torque for opening the valve.
It is also desired to provide a reliable seal for rotary valves which can be reliably used in bi-directional flow applications.
It is further desired to provide a valve which can meet fire-test specifications and which can maintain a positive fluid shutoff condition even when high temperatures and fires may have reduced the effectiveness or destroyed any Teflon or other resilient material sealing rings. In particular it is desired to provide a valve which meets the fire-test requirements in both flow directions.